Occupant restraining systems represented by seat belts and air-bag systems have become smaller and of lower cost, and are nowadays installed in almost all kinds of vehicles as standard equipment. This kind of occupant restraining system should be able to detect the occupant of a seat with accuracy for urging him/her to wear the seat belt or for controlling the air-bag according to the presence/absence of the occupant.
On the other hand, vehicles used in cold climates sometimes have a heating element installed in the seats for warming the occupants. The seats of vehicles generally have a seat surface made of a low heat conductive material such as urethane foam. Therefore, for warming the occupant efficiently, the heating element should be placed near the seat surface.
Then, a two-tier structure unit formed by laminating a heating element film and a sensor film has been proposed (for example, see Japanese National Patent Publication No. 2004-504082).